The present invention relates to a device for releasing a parachute.
An electronic device for releasing a parachute is known from U.S. Pat. No. 4,858,856. According to this known device, a pressure sensor is used for determining the initial altitude value and for determining further pressure values. When a predetermined pressure has been reached, the device will release the parachute if a predetermined pressure change rate has been exceeded. Since the speed of a falling object depends from a number of parameters, such as for example the weight of the object attached to the parachute, the air resistance of the object, ect. the known device is not very accurate.
This problem of accuracy has been solved with the device according to EP-A-0 785 130 by using an accelerometer in addition to a pressure sensor. Such a device is however more cumbersome and expensive.
The object of the invention is to provide an alternative device for releasing a parachute which is still reliable and relatively inexpensive.
To this object, the device for releasing the parachute according to the invention comprises a data processing system having a release signal output and a memory provided for storing data, said data processing system being provided for generating a release signal for opening said parachute; altitude determining means connected to said data processing system and provided for determining altitude values; and time determination means provided for determining the free fall duration as from the start of the dive. Said memory is provided for storing a plurality of series of theoretical dive data, said theoretical dive data indicating for each distance value a corresponding theoretical time. Said data processing system is further provided for selecting a series of theoretical dive data in function of the determined altitude values and the determined free fall duration.
In particular, said distance value indicates a fall distance and said theoretical time indicates a free fall duration. According to an alternative, said distance value indicates an altitude value and said theoretical time indicates a theoretical free fall remaining time. The data processing system is provided for selecting a series of theoretical dive data in function of the determined altitude values and the determined free fall duration by performing the following steps. A default series of theoretical dive data among said series of theoretical dive data is selected as active series of theoretical dive data. An initial altitude value (hn,ini) is stored when said dive is started. On the basis of said active series of theoretical dive data and said initial altitude value, an initial theoretical free fall remaining time (trem,theor,ini) is determined. On the basis an actual altitude value (hn) and the initial altitude value (hn,ini) the corresponding fall distance (xcex94hfall) is determined. On the basis of said active series of theoretical dive data and said fall distance (xcex94hfall) a theoretical free fall duration (tfall,theor) is determined. A sum of a predetermined number of differences between said theoretical free fall duration (tfall,theor) with the free fall duration (tfall,meas) determined with the time determination means is determined. Upon establishing that said sum exceeds a threshold value, a further series of theoretical dive data is selected as active series of theoretical dive data. Said release signal is generated when said determined free fall duration reaches said initial theoretical free fall remaining time and a given altitude change rate is exceeded.
According to an alternative, said distance value indicates an altitude value and said theoretical time indicates a theoretical free fall remaining time. In that case, the theoretical free fall duration (tfall,theor) is determined by first determining on the basis of the active theoretical dive data, the corresponding theoretical free fall remaining time (trem,theor) and then on the basis of the initial theoretical free fall remaining time (trem,theor,ini) and the corresponding theoretical free fall remaining time (trem,theor).
The device according to the invention allows to switch from one series of theoretical dive data to another series, which will better match with the measured data. This allows to determine more accurately the remaining free fall time.
The predetermined number of differences can be equal to one. However, for increasing the accuracy of the results, the predetermined number is at least 3, and preferably at least 10.
Preferably, the device further comprises means for generating a further warning signal upon establishing that said determined altitude value has crossed a threshold altitude value. This informs the user, upon climbing, that the device is operating properly.
Before releasing the parachute, it is desirable to warn the skydiver that he approaches the danger altitude at which the parachute should be opened. This is achieved by providing that the device further comprises means for generating a warning signal upon establishing that the difference between the initial theoretical free fall remaining time and the determined free fall duration has reached a threshold duration value.
Selection of different default theoretical dive data is achieved by providing that the device further comprises means for selecting a jump mode, each jump mode being dedicated to default theoretical dive data. Preferably, said given altitude change rate is in function of the selected jump mode. This enables to differentiate a dangerous situation between a student, an expert and tandem skydivers.